Question

If 10 20 molecules are removed from 3.4 mg of ammonia then the number of moles of ammonia left are

Answer 1

Answer: The number of ammonia molecules left are $2.044\times 10^{19}$

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Mass of ammonia = 3.4 mg = $3.4\times 10^{-3}g$      (Conversion factor: 1g = 1000 mg)

Molar mass of ammonia = 17 g/mol

Putting values in above equation, we get:

$\text{Moles of ammonia}=\frac{3.4\times 10^{-3}g}{17g/mol}=0.2\times 10^{-3}moles$

According to mole concept:

1 mole of a compound contains $6.022\times 10^{23}$ number of molecules.

So, $0.2\times 10^[-3}$ moles of compound will contain = $0.2\times 10^{-3}\times 6.022\times 10^{23}=1.2044\times 10^{20}$ number of molecules.

Number of molecules removed from ammonia = $10^{20}$

Amount of molecules left will be = $(1.2044-1)\times 10^{20}=0.2044\times 10^{20}=2.044\times 10^{19}$

Hence, the number of ammonia molecules left are $2.044\times 10^{19}$

Answer 2

Answer: 2.044×10^19

Explanation:

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